Colonel Nathaniel Littleton *did* have an older sister Mary - but she stayed home in Wales and married one Gilbert Jones. This has been ascertained from *primary* documentation, not "family lore".
It is not quite certain whether Col. Scarburgh's wife was a Cade, a Harmar, a Cade widow of a Harmar, or a Harmar widow of a Cade. But she was not a Littleton and had nothing to do with the Littleton family.
The cause for all the confusion is his son "Littleton Scarburgh" - who was NOT given his mother's maiden name, but his *godmother's married name*. His godmother was Ann (Southy) Littleton, wife of Colonel Nathaniel Littleton, and she may have suggested the name (a privilege sometimes accorded to godparents).